1. Field of the Invention
The present invention relates generally to the detection of ethanol and/or acetone. The present invention relates more particularly to the film bulk acoustic wave resonator-based devices, and their use in the sensing of ethanol and/or acetone.
2. Technical Background
Driving under the influence of alcohol is a serious traffic violation; such behavior causes many accidents and deaths on the road. Electrochemical breath alcohol analyzers are generally used as a quick and reliable screening device at sobriety checkpoints and after motorists are pulled over on suspicion of DUI. However, acetone can strongly interfere with electrochemical detection. Acetone is generally considered to be the only endogenous volatile organic compound that is a potentially interfering substance in breath alcohol analysis. It is present in the breath of a normal person, and in increased concentrations as the result of prolonged fasting, use of ketogenic diets, or diabetes. Moreover, breath acetone itself can be an analyte of interest for medical diagnostic purposes. The analysis of exhaled breath for acetone can help to provide an express non-invasive diagnosis of ketosis.
In conventional sensors, ethanol and acetone can interfere with one another. Accordingly, drunkenness can wrongly be interpreted as ketosis, and vice versa. Ethanol and acetone can be distinguished using electrochemical or infrared instruments in commercial breath alcohol analyzers. However, they are complex and expensive, and specific training is required in order to become a proficient user. Resistivity-based metal oxide sensors have been developed, which can have relatively simple structures and can be cost effective and easy to use. Their main drawback is that they can not effectively distinguish ethanol and acetone. Because they use the change in resistivity as the gas detecting signal, both ethanol and acetone will share a similar response: a decrease in resistivity. Resistivity-based ethanol sensors based on zinc oxide thin films have been extensively investigated. Special attention is given to discriminating between ethanol and acetone due to their similar chemical nature. However, as both gases can reduce the resistivity of the sensor, the selectivity was not as high as desirable. Selected ion flow tube mass spectrometry has shown great potential in real-time concentration monitoring of acetone and ethanol in human breath. While it is highly selective and sensitive, its high cost and limited portability hinder its usefulness as a standard diagnostic tool.